Injuries to soft tissue, such as cartilage, skin, muscle, bone, tendon and ligament, where the tissue has been injured or traumatized frequently require surgical intervention to repair the damage and facilitate healing. Such surgical repairs can include suturing or otherwise repairing the damaged tissue with known medical devices, augmenting the damaged tissue with other tissue, using an implant, a graft or any combination of these techniques. Despite these conventional methods of tissue repair, there is a continuing need in this art for novel surgical techniques for the surgical treatment of damaged tissue (e.g., cartilage, meniscal cartilage, ligaments, tendons and skin) that can effect a more reliable tissue repair over the long term and can facilitate the healing of injured tissue.
Recently, tissue engineering approaches to repairing tissue damage or injury have been used with increasing frequency. These methods typically involve replacing or reconstructing damaged or injured tissue with cells capable of new tissue growth. The cells are usually incorporated into a delivery vehicle such as a surgical implant for placement at the tissue site, whereupon the healthy cells can grow into their surrounding environment. Various surgical implants are known and have been used in surgical procedures to help achieve these benefits. For example, it is known to use various devices and techniques for creating implants having isolated cells loaded onto a delivery vehicle. Such cell-seeded implants are used in an in vitro method of making and/or repairing cartilage by growing cartilaginous structures that consist of chondrocytes seeded onto biodegradable, biocompatible fibrous polymeric matrices. Such methods require the initial isolation of chondrocytes from cartilaginous tissue prior to the chondrocytes being seeded onto the polymeric matrices. Other techniques for repairing damaged tissue employ implants having stem or progenitor cells that are used to produce the desired tissue. For example, it is known to use stem or progenitor cells, such as the cells within fatty tissue, muscle, or bone marrow, to regenerate bone and/or cartilage in animal models. The stem cells are removed from the animal and placed in an environment favorable to cartilage formation, thereby inducing the fatty tissue cells to proliferate and to create a different type of cell, such as cartilage cells.
While the trend towards using tissue engineering approaches to tissue repair continues to gain popularity, mainly because of the long-term benefits provided to the patient, these current techniques are not without drawbacks. One disadvantage with current tissue engineering techniques is that they can be time consuming. A typical process involves the harvest of cellular tissue in a first surgical procedure, which is then transported to a laboratory for cell culturing and amplification. The tissue sample is treated with enzymes that will release the cells from the matrix, and the isolated cells will be grown for a period of 3 to 4 weeks using standard cell culture techniques. Once the cell population has reached a target number, the cells are sent back to the surgeon for implantation during a second surgical procedure. This manual labor-intense process is extremely costly and time consuming. Although the clinical data suggest long term benefits for the patient, the prohibitive cost of the procedure combined with the traumatic impact of two surgical procedures, has hampered adoption of this technique.
The current model for tissue repair generally involves retrieving a cell sample from a patient, isolating the cells, culturing the cells for several weeks, and then implanting them in a defect, either with or without a scaffold. Preferably, a scaffold is used in order to facilitate newly developing cell growth. In the past, such scaffolds have consisted mostly of two- or three-dimensional porous scaffolds that allow cell invasion and remodeling once the scaffold has been combined with living cells and has been delivered inside the patient. This model is limited in application because of the secondary surgery and high costs involved. More importantly, one limitation of using such scaffolds is that tissue defect geometry can often be unpredictable. Since the scaffold geometry is essentially limited to what has been manufactured, the scaffold carrier to be implanted rarely matches perfectly the site. In order to achieve a desirable complementary fit with the defect or injury site, the scaffold often needs to be revised by trimming prior to or after implantation. This additional adjustment time adds onto the overall surgery time for the patient. For certain difficult to match or unusually shaped sites, even the step of trimming the scaffold does not ensure an ideal fit with the implantation site. Further, where relatively large tissue defects are involved, minimally invasive surgery may not be possible due to the limited size of the surgical access site. Therefore, delivery of large scaffolds may require an open procedure which poses more risks to the patient.
Injectable gels and microcarrier beads have also been used in the past as cell delivery vehicles. These systems have the advantage of sometimes being injectable and therefore require less invasive procedures for implantation. Typically, these carriers have been combined with isolated cells, which are sensitive to manipulation such as shear, or the presence of crosslinkers that are required to allow the carrier to be fixed or set in place. Hence, these systems have proven to be less than ideal due to the problems associated with cell viability once incorporated into these carrier systems. Accordingly, there continues to exist a need in this art for a method of delivering tissue repair implants through a minimally invasive procedure. Also desirable is a conformable tissue repair or augmentation implant that can adapt to the shape or geometry of the tissue site. The implant should be suitable for delivering viable tissue capable of effecting new cell growth. It is also desirable to provide a method for making such an implant, whereby the implant can be made in a quick and efficient manner for immediate use during surgery.